Photolithography or optical lithography systems used in the manufacture of integrated circuits have been around for some time. Such systems have proven extremely effective in the precise manufacturing and formation of very small details in the product. In some photolithography systems, a circuit image is written on a substrate by transferring a pattern via a light or radiation beam (e.g., UV or ultraviolet light). For example, the lithography system may include a light or radiation source that projects a circuit image through a reticle and onto a silicon wafer coated with a material sensitive to irradiation, e.g., photoresist. The exposed photoresist typically forms a pattern that after development masks the layers of the wafer during subsequent processing steps, as for example deposition and/or etching.
In one metrology technique, characterization of the quality of printed patterns, such as periodic gratings, on a semiconductor wafer can be determined by collecting critical dimension scanning electron microscope CD-SEM images at each location on the wafer and examining each image for pattern quality. This technique is time consuming (e.g., several hours), and judgments about grating quality may currently be somewhat subjective. The CD˜SEM measurement also fails to provide information as to the subsurface defect structure.
In view of the foregoing, improved apparatus and techniques for characterization of printed patterns are desired.